The present invention relates to a gas fire fighting system for extinguishing fire by discharging inert gas fire extinguisher stored in a gaseous state in fire extinguisher storage vessels into the object fire fighting section, and maintaining the concentration of the fire extinguisher in the object fire fighting section at no less than a fire extinguishing concentration.
Conventionally, equipment using inert gas such as carbon dioxide, halogenated gas, etc. as fire extinguisher has been put in to practical use as a gas fire fighting system for extinguishing fire by discharging the gas fire extinguisher into an object fire fighting section and maintaining the concentration of the fire extinguisher in the object fire fighting section at no less than a fire extinguishing concentration.
When inert gas such as carbon dioxide, halogenated gas, etc. are used as fire extinguishers, the fire fighting system is designed in such a way as to liquefy the fire extinguishers under pressure and store them in fire extinguishing equipment in a charged state in a fire extinguisher storage vessel composed of a high-pressure gas vessel. In case of a fire, the carbon dioxide or halogenated gas is sent from the fire extinguisher storage vessel to an injection head through piping by opening a vessel valve of the fire extinguisher storage vessel by using an appropriate electrical means or pneumatic means and discharging it from the injection head into the object fire fighting section. At that time, the inert gas, such as carbon dioxide, halogenated gas, etc. is sent in a liquid state up to the injection head and, the moment when it is discharged from the injection head into the object fire fighting section, it is vaporized and gets into a gaseous state so as to fill the object fire fighting section and extinguish the fire.
The gas fire fighting system using inert gas such as carbon dioxide, halogenated gas, etc. is widely used not only in oil facilities and with electric equipment, but also in other general facilities, because of advantages such that it can rapidly extinguish fire, hardly stains the inside of the object fire fighting section with the fire extinguisher, does not spoil electric insulation, demonstrates powerful fire extinguishing effects even against an object of fire fighting of complicated structure, as the fire extinguisher penetrates through gaps, maintains a certain level of fire extinguishing capacity over a long period of time with no change of fire extinguisher, etc.
However, in recent years, problems regarding ozone layer depletion have arisen on a worldwide scale, and the production of fire extinguishers containing halogenated hydrocarbon components, such as halogenated gas, etc., was discontinued in January, 1994, making such fire extinguishers practically unusable. As a result, carbon dioxide has become the only fire extinguisher currently in use for gas fire fighting systems, except for special fire fighting systems using expensive rare gases such as argon, etc.
On the other hand, this fire fighting system using carbon dioxide is also known to have the following problems:
(1) The design concentration of carbon dioxide in the object fire fighting section at the time of fire fighting is approximately 35%. At this concentration, there is a possibility of producing a serious state claiming human life due to the toxicity (anesthetization) of carbon dioxide in case there is someone in the object fire fighting section.
(2) In case of a fire, the carbon dioxide is sent to the injection head in a liquid state and turns into a gas by evaporation the moment when it is discharged into the object fire fighting section. At that time, carbon dioxide absorbs heat of evaporation from the surrounding air, making the saturated vapor pressure of the room air drop, causing dew condensation of water content in the air and producing static electricity. As a result, the room air becomes hazy and presents a risk of serious secondary disasters by not only creating obstacles to evacuation and relief of people and fire fighting, but also causing defective insulation or trouble with electric equipment due to dew condensation or static electricity.
(3) Because carbon dioxide has a density much higher than that of air, the carbon dioxide discharged into the object fire fighting section is liable to not only stagnate in the lower part in the object fire fighting section and deteriorate in its fire extinguishing effects, but also disperse to the outside through openings at the bottom of the object fire fighting section.
(4) In view of the fact that problems of the greenhouse effect on the earth are being discussed on a worldwide scale, there is a possibility that the use of carbon dioxide may also be restricted in the future, in the same way as halogenated gas.
By the way, the assignee of the present invention previously proposed a fire fighting system using as fire extinguisher nitrogen gas or a mixed gas (hereinafter simply referred to as "mixed gas") prepared by mixing at least one kind of perfluoroalkane (perfluorobutane (C.sub.4 F.sub.10)), hydrogenofluoroalkane (trifluoromethane (CHF.sub.3), heptafluoropropane (C.sub.3 HF.sub.7), pentafluoroethane (C.sub.2 HF.sub.5), or hydrogenefluorohalogenoalkane (iodotrifluoromethane (CF.sub.3 I) (hereinafter generically referred to as "fluoric compounds") in nitrogen gas at a proportion no higher than 10 vol. %, to solve a lot of problems inherent in the gas fire fighting systems (Japanese Patent Application Publication Nos. 08-141102 and 08-243186).
However, it has been found that the following problems exist even in the case where nitrogen gas or mixed gas are used as fire extinguisher of gas fire fighting systems:
(1) Nitrogen gas or mixed gas used as fire extinguisher of gas fire fighting systems are stored in a state of pressurized gas, and therefore require a number of fire extinguisher vessels necessary for fire extinction of an object fire fighting section of a volume several times larger as carbon dioxide or halogenated gas, which are in a liquefied state due to pressurization, and thus require a large installation space for the fire extinguisher vessels.
(2) To reduce the number of fire extinguisher vessels to be installed, it is necessary to increase the charging pressure of the inert gas fire extinguisher to be charged in the fire extinguisher vessels. However, if the charging pressure of the inert gas fire extinguisher is increased, the high gas pressure of the inert gas fire extinguisher comes to be applied also to the secondary side equipment of the fire fighting system, such as a selecting valve, main piping, a branch pipe, an injection head, etc. This makes it necessary to increase the pressure resistance grade of those secondary side equipment units, thus leading to a sharp increase in equipment costs, and also making the application to existing facilities impossible.